In today's minimally invasive surgeries, imaging devices are used to help a surgeon visualize the interior of a patient's body. Depending on the type of procedure, an endoscope is typically inserted into the patient's abdominal area, knee joint, shoulder joint or some other part of the body that requires surgical treatment. As shown in prior art FIG. 1, the endoscope 12 is usually connected at its proximal end to a camera 14 which is connected to an image processing device 16 either via a connecting cable 18 or wirelessly through a radio frequency transmitter and receiver (not shown). The camera 14 usually contains image sensors, such as CCD, CMOS or other kinds of imaging devices. As shown in FIG. 1, an external light source 20 is also usually connected to the endoscope 12 by a fiber optic cable 22. The processing device 16 and light source 20 are shown on shelf unit 23.
As shown in FIG. 2, the endoscopes 12 used in today's minimally invasive surgeries have a circular outer shield 24 and a circular optical system 26 inside the outer shield 24 to transmit an image from a distal end 28 to a proximal end 30. The outer shield 24 is typically stainless steel or a flexible plastic material. The circular optical system 26 generally is either a series of rigid rod lenses or a flexible optical fiber inserted along the longitudinal axis of the endoscope 12. These endoscopes have not changed much over the last decade or so in terms of the way they pick up and transmit an image of a target object from the distal end 28 of the endoscope 12 through the optical system 26 and an optics coupler 34 to image sensors 36 of the camera 14 at the proximal end 30 of the endoscope 12. The circular optical system 26 views objects in the field of view 38 as shown in FIG. 2. An image enters the distal end 38 of the endoscope 12 and travels through circular optical system 26 and optics coupler 34 to the image sensor 36 at the proximal end 30 of the endoscope. Fiber optic cable 22 provides light from light source 20 to a light transmitting optic fiber 40 that outputs illuminating light at the distal end 28 of the endoscope 12. While a single optic fiber 40 is shown, a plurality of optic fibers may output light at the distal end 28 of the endoscope 12.
Prior art endoscopes are initially designed to be used with imaging elements of standard definition (SD) aspect ratio. Such an aspect ratio is also known as 4:3 or 5:4, which is the fraction of the horizontal width of a video image to the vertical height of the image on a display device. Imaging technology and consumer demand, however, have significantly changed recently and the aspect ratio requirement for such endoscope video systems has shifted from the standard definition (SD) aspect ratio to wide screen (also known as high definition (HD) aspect ratio which is typically a width to height ratio of 16:9.
In addition to a wider aspect ratio, advancements in imaging technology have led to higher native acquisition resolutions in both interlaced and progressive scanning modes. Interlaced or progressive scanning usually refers to the way an image is acquired by the image sensor. If the horizontal lines of image are scanned one after another consecutively, then the system is called a progressive scan system. If the horizontal lines of image are scanned by skipping every other line in the first scan followed by a second scan to scan the skipped lines, then the system is called an interlaced scanning system. Whether an interlaced or a progressive scan, the HD resolution includes at least one of the following three well known standards: 1280×720p, 1920×1080i, and 1920×1080p, where i stands for interlaced and p stands for progressive. Although these three formats may have different horizontal and vertical lines of resolution, they all maintain a 16:9 horizontal to vertical aspect ratio. Also known as HDTV standards, these three standards are perceived to show more picture and better picture quality on a display screen. Typically, however, progressive scan systems provide a superior image quality compared to interlaced scan systems. Movies and sports events primarily benefit from these HDTV standards, especially the progressive scan ones, which give a unique viewing angle and feel to their viewers.
Since the imaging and display technologies have advanced from standard definition (SD) resolutions (with 4:3 or 5:4 aspect ratio) to high definition (HD) resolutions (with 16:9 aspect ratio), almost all consumer-grade imaging equipment has shifted over to using a 16:9 aspect ratio. The same technological change has also been affecting the medical markets including endoscopic imaging equipment. The image sensor devices (primarily CCD and CMOS sensors or devices performing a similar function) and the displays (LCDs and plasma screens) have slowly shifted toward a 16:9 aspect ratio in endoscopic imaging applications.
Existing scopes, as used with the existing 4:3 aspect ratio imaging sensors as described above, cause significant loss of viewing area as shown in FIG. 3. The magnified scope image 42 shown in FIG. 3 covers and extends beyond the usable surface area of the generally rectangular imaging device 44 due to the simple geometrical mismatch of the endoscope's circular optical element with a rectangular 4:3 aspect ratio imaging element. Thus, this arrangement shows a problem that already existed with 4:3 aspect ratio imaging elements 44. The mismatch, however, becomes much more unacceptable and undesirable with the use of a HD imaging device 46 having a 16:9 aspect ratio as shown in FIG. 4. Although a 16:9 rectangular imaging device 46 can cover more of the scope's circular image 42 from side to side as compared to a 4:3 imaging device, the 16:9 imaging device 46 receives much less of the scope's circular image 42 vertically upwardly and downwardly compared to the 4:3 imaging device 44 as shown by comparison of FIG. 4 with FIG. 3. In other words, an imaging device 46 having a 16:9 aspect ratio does not maximize the amount of a circular image 42 that can be viewed from an endoscope imaging arrangement. Instead, less of the vertical portions of the image 42 are viewable. This invention offers a solution to minimize or eliminate the problem.
One device that addresses the problem is disclosed in U.S. Pat. No. 6,498,884 to Colvin, et al., whose disclosure is incorporated herein by reference. In the '884 system, multiple rectangular optical channels (lens elements) are used to create an overall rectangular lens system. This arrangement also requires all sides of the individual rectangular lenses to be coated or blackened to minimize glare and refractive errors. Besides the excessively high cost of manufacturing rectangular lenses, such designs usually continue to have optical image quality problems due to the natural corners of the rectangular lens elements no matter what kind of coating is provided for the rectangular lenses. In fact, perfectly coating such lens corners in practical systems is almost impossible. The invention described herein does not require any of the above special requirements and uses readily available rounded optical rod elements and optical fibers or the like.
Another wide viewing endoscope is taught in U.S. Patent Publication 2006/0235276 A1. The '276 publication discloses an endoscope having a plurality of illumination lenses and one objective viewing lens having a wide angle.